remove code that doesn't seem necessary anymore on iOS8
Use different variables to get viewport size.
Seems better on iOS.

But on the popup.html test, there are problems if

1. you click "show centered dialog"
2. focus the input
3. click the "show popup" button (within the dialog)

Focus goes back to the input.
activationTracker: increase window where blur event ignored.

In the popup.html test on my iPad I was seeing a case where the tooltip popup would incorrectly close:

1. open the tooltip dropdown
2. focus the input
3. click a button in the tooltip

The blur event on the input came > 100ms after the pointerdown event.
Perhaps just because I was tethered to my mac and using the debugger.
popup: split position and size into separate methods
debugging statements
Add workaround code for when iOS problem
where clicking the <button> below the <input> just refocuses the input,
apparently due to the browser's auto-scrolling.